The invention relates to a sealing cap for the fuel tank pipe for motor vehicles, with an outer cap and an inner cover portion, held in torsion-proof relationship therein, whereby the inner cover portion being cup-shaped, having a peripheral flange at its side which faces the outer cap and bearing packing means for the sealing of the pipe and comprising fastening means for engagement with the pipe, the outer cap at its reverse side, facing the inner cover portion, including an integrally molded rib of a synthetic material, having at its free end at least one inwardly-directed radial lug engaging the inner cover portion, and the outer cap being adapted to snap off from the inner cover portion whenever the outer cap is affected by forces such as they occur during a motor vehicle accident.